Range over which plants continue to grow 100 o Birch(B. occidentalis) 80 Maple(A grandidentatum) 40 20 d -----Dehydration Air injection 0 0.01.02.0304.05.06.0708.09.0 Injection pressure or-xylem pressure(MPa)
2.3.3 Embolized xylem can be repaired e Several mechanisms can raise the pressure within gas-filled xylem vessels to values ranging from slightly negative to positive. o The increased pressure augmented by the additional pressure exerted by sur face tension in small bubbles can be sufficient to drive the gas back into solution o In herbaceous species, nightly root pressure can play an essential role in reversing daily cavitation o Curiously, embolized xylem can also become recharged during periods of substantial xylem tension. The mechanism involved unclear, although most hypotheses envision an active role for the xylem parenchyma in solute secretion and water movement into embolized vessels
2.3.3 Embolized xylem can be repaired ⚫ Several mechanisms can raise the pressure within gas-filled xylem vessels to values ranging from slightly negative to positive: ⚫ The increased pressure augmented by the additional pressure exerted by surface tension in small bubbles can be sufficient to drive the gas back into solution. ⚫ In herbaceous species, nightly root pressure can play an essential role in reversing daily cavitation. ⚫ Curiously, embolized xylem can also become recharged during periods of substantial xylem tension. The mechanism involved is unclear, although most hypotheses envision an active role for the xylem parenchyma in solute secretion and water movement into embolized vessels
Xylem tension can be measured with the pressure bomb Pressure inside the conducting cells =-1. 0 MPa Rubber Pressure source (tank of compressed air o nitrogen) Pressure gauge Pressure Air pressure =0 MPa +1.0 MPa Pressure release valve
Xylem tension can be measured with the pressure bomb
2. 4 Water transport through aquaporins o 2. 4. 1 Membrane permeability to water can be defined with either an osmotic coefficient (Pf or a diffusional coefficient (Pd)
2.4 Water transport through aquaporins ⚫ 2.4.1 Membrane permeability to water can be defined with either an osmotic coefficient (Pf ) or a diffusional coefficient (Pd )
The osmotic coefficient for water permeability(Pf)of plant membranes can be determined Ca illary tube (calibrated for volume) Air bubble ea Cell Open chamber Closed chamber
The osmotic coefficient for water permeability (Pf) of plant membranes can be determined